Choanocyte Chambers Research Articles

Sycetta papillata sp. nov. (Porifera, Calcarea): the first record of Sycetta to the Southwestern Atlantic Ocean

Sycetta is a poorly known genus of calcareous sponges, primarily distinguished by the presence of tubes (the choanocyte chambers) radially organized around the atrial cavity and completely separated from each other. These tubes, referred to as conical diverticula or more aptly as papillae, impart a distinctive appearance to the external morphology of the sponges. Herein, we present the description of Sycetta papillata sp. nov., based on the examination of specimens collected several decades ago in the state of Bahia, located in Northeastern Brazil. The presence of a single category of diactines and atrial region formed exclusively by tetractines makes this species unique within the genus. While some species of Sycetta have been documented in deep regions, exceeding depths of 200 meters, the distribution range of S. papillata sp. nov. spans from 0.5 to 25 meters in depth. A comparative table of Sycetta species is being provided.

Insight on thermal stress response of demosponge Chondrosia reniformis (Nardo, 1847)

Global warming has led to an increase in extreme weather and climate phenomena, including floods and heatwaves. Marine heatwaves have frightening consequences for coastal benthic communities around the world. Each species exhibits a natural range of thermal tolerance and responds to temperature variations through behavioral, physiological, biochemical, and molecular adjustments. Physiological stress leading to disease and mass mortality appears when tolerance thresholds are exceeded. Sessile species are therefore particularly affected by these phenomena. Among these sessile species, marine sponges are important members of coral reef ecosystems. To better understand the sponge thermal stress response, we tested the response of demosponge Chondrosia reniformis (Nardo, 1847) to three different temperatures (8 °C, 24 °C and 30 °C) during two exposure periods of time (4 and 14 h). Histological studies of whole parts of the sponge, biochemical analyses (Defense enzymes) and gene expression levels of some target genes were undertaken in this study. The exposure to cold temperature (8 °C) resulted in inhibition of antioxidant enzymes and less modification in the gene expression level of the heat shock proteins (HSPs). These latter were strongly upregulated after exposure to a temperature of 24 °C for 4 h. However, exposure to 30 °C at both periods of time resulted in indication of HSP, antioxidant enzymes, the gene involved in the apoptosis process (Bcl-2: B-cell lymphoma 2), the gene involved in inflammation (TNF: Tumor Necrosis Factor), as well as the aquaporin gene, involved in H2O2 permeation. Moreover, the normal organization of the whole organism was disrupted by the extension and fusion of choanocyte chambers and alteration of the pinacoderm. Interestingly, exposure to sublethal temperatures may show that this sponge has an adaptation threshold temperature. These insights into the adaptation mechanisms of sponges contribute to better management and conservation of sponges and to the prediction of ecosystem trajectories with future climate change.

Choanocyte dimensions and pumping rates in the demosponge Halichondria panicea

The individual choanocyte pumping rate in choanocyte chambers (CCs) is important for understanding the hydrodynamics in sponges and has hitherto been based on measured volume-specific filtration rate and estimated CC density. However, the CC density may vary in different regions of the sponge and to circumvent this uncertainty and to get precise measurements of the individual choanocyte pumping rate, a new experimental approach was developed. Here the aim was to measure the individual pumping rate of choanocytes based on live dimensions of CC elements and particle tracking to measure the speed of small particles entering into the CCs. This was done by using combined live-cell imaging in sandwich cultures of the marine demosponge Halichondria panicea and video-tracking of particles. Small 2 μm-beads and cyanobacteria (Cyanobium bacillare) in the incurrent canal enter the CCs via a 3.3 ± 0.9 μm diameter prosopyle to be subsequently captured by the choanocytes whereas larger algal cells (Rhodomonas salina) and 10 μm-beads are captured in the incurrent canals. CC diameters were positively correlated to the diameter of choanocytes, indicating a total of 84 choanocytes per CC with mean diameter 22.9 ± 6.2 μm. The pumping rate per choanocyte (Qc) was estimated to be between 54 and 68 μm3 s−1. Regardless of demosponge species and based on data in the literature, a choanocyte is suggested to pump between 50 and 100 μm3 s−1.

Fate of microplastic captured in the marine demosponge Halichondria panicea

Microplastic particles are widespread pollutants in the sea and filter-feeding sponges have recently been suggested as useful monitoring organisms. However, the fate of microplastic particles in sponges is poorly understood, yet crucial for interpreting monitoring data. The present study aims to help develop sponges as more useful monitoring organisms for microplastic in the sea. Here, we describe the fate of inedible (2 and 10 μm) plastic beads compared to that of edible bacteria and algal cells captured in the marine demosponge Halichondria panicea. Small Cyanobium bacillare cells entered the choanocyte chambers and were phagocytized by choanocytes, while larger Rhodomonas salina cells were captured in incurrent canals and phagocytized in the mesohyl. Small 2 μm-beads were captured by choanocytes and subsequently expelled into the excurrent canals after 58 ± 34 min. Larger 10 μm-beads were captured in the incurrent canals and transferred to the mesohyl, where amoeboid cells moved them across the mesohyl before they were expelled into the excurrent canal after 95 ± 36 min. SEM observations further indicated engulfment of plastic beads on the outer sponge surface. This insight provides useful information on how sponges, in general, treat microplastic particles of various sizes. It helps us understand actual measured sizes and concentrations of microplastic particles in sponges in relation to those in the ambient water.

Hydrodynamics in early animal evolution.

Choanoflagellates and sponges feed by filtering microscopic particles from water currents created by the flagella of microvillar collar complexes situated on the cell bodies of the solitary or colonial choanoflagellates and on the choanocytes in sponges. The filtering mechanism has been known for more than a century, but only recently has the filtering process been studied in detail and also modelled, so that a detailed picture of the water currents has been obtained. In the solitary and most of the colonial choanoflagellates, the water flows freely around the cells, but in some forms, the cells are arranged in an open meshwork through which the water can be pumped. In the sponges, the choanocytes are located in choanocyte chambers (or choanocyte areas) with separate incurrent and excurrent canals/pores located in a larger body, which enables a fixed pattern of water currents through the collar complexes. Previous theories for the origin of sponges show evolutionary stages with choanocyte chambers without any opening or with only one opening, which makes separation of incurrent and excurrent impossible, and such stages must have been unable to feed. Therefore a new theory is proposed, which shows a continuous evolutionary lineage in which all stages are able to feed by means of the collar complexes.

Oogenesis and embryogenesis in a cryptogenic species of calcareous sponge (Calcaronea, Heteropiidae) in the southwestern Atlantic

AbstractCalcarea is a diverse group of sponges, in which individuals are generally small and found in cryptic habitats. These characteristics hamper the access to them and, consequently, the knowledge about several aspects of their biology, including reproduction. Little is known about many reproductive aspects of these sponges and broad generalizations are made upon few studied species. Therefore, investigations dealing with the oogenesis and embryogenesis of more species are still necessary. Sycettusa hastifera is an alien species in the southwestern Atlantic. Knowledge about its reproduction would not only help to improve our comprehension of reproduction in Calcaronea but would also help to understand the capacity of this exotic species to colonize. Histological and electron microscopy analyses of individuals sampled at Arraial do Cabo (Rio de Janeiro, Brazil) showed that oogenesis in S. hastifera was long (4–6 months) and nutrients were acquired by association with nurse cells and endocytosis of bacteria, yielding heterogeneous and complex yolk inclusions. Cleavage, inversion, and amphiblastula larvae were similar to what has been observed in other calcaroneans, except for the larval cavity lacking amoeboid cells and the relatively long swimming period of the amphiblastula (on average 12 h, but reaching 72 h). Our results indicate that the vitellogenic mechanism characterized as mixed (an ancestral characteristic of Calcaronea) is strongly influenced by autosynthesis; during cleavage, cell fates could be determined from embryo to larva; and inversion of the embryo (which will become the amphiblastula larva) directly into the choanocyte chamber is an ancestral characteristic of Calcaronea. Despite the absence of amoeboid cells or other structures to nourish the larva, the long swimming period suggests that vitellogenesis is sufficient for the maintenance of the embryo and larva until metamorphosis. This characteristic may facilitate the spread of this cryptogenic species to new regions.

Fine details of the choanocyte filter apparatus in asconoid calcareous sponges (Porifera: Calcarea) revealed by ruthenium red fixation

Sponges (phylum Porifera) are highly specialized filter-feeding metazoans, pumping and filtering water with a network of canals and chambers, the aquiferous system. Most sponges have a leuconoid aquiferous system, characterized by choanocytes organized in small spherical chambers connected with ambient water by a complex net of canals. Such organization requires substantial pressure difference to drive water through an elaborate system of canals, so the choanocytes in leuconoid sponges have several structural features to generate pressure difference. In contrast, it is generally accepted that asconoid and syconoid sponges with long choanocyte tubes or large choanocyte chambers have no similar structures in their choanocytes. The present study is devoted to the detailed ultrastructural analysis of the choanocytes and their filter apparatus in the asconoid calcareous sponge Leucosolenia variabilis. The general structure of L. variabilis choanocytes is similar to that described for other sponge species. However, the fixation with 0.1% ruthenium red allowed us to reveal for the first time a complex of glycocalyx structures (vanes on the flagella, a fine glycocalyx sealing microvilli in the collar, and a glycocalyx strainer, embedding the apical parts of neighboring collars) in the choanocytes of L. variabilis, which are traditionally associated with the pumping and filtration process in leuconoid demosponges. All revealed glycocalyx structures have dimensions and locations similar to those found in the choanocyte chambers of some demosponges. The data suggest that L. variabilis utilizes the principles of water pumping and filtration similar to those in demosponges and revealed glycocalyx structures are potentially crucial for these processes. It seems that sponges from distant phylogenetic lineages and with different body plans rely on common principles of choanoderm organization for effective pumping and filtration of water. However, while some adaptation for effective pumping and filtration of water have possibly arisen before the diversification of Porifera, others have appeared independently in different lineages.

Differences in the Structural Components Influence the Pumping Capacity of Marine Sponges

Marine sponges are important sessile, benthic filter feeders with a body plan designed to pump water efficiently. The sponge body plan generally consists of mineral spicules, gelatinous mesohyl, and the pores and canals of the aquiferous system. These structural components have stark differences in compressibility, mass, and volume; therefore, their proportion and distribution are likely to affect sponge morphology, anatomy, contraction, and finally the pumping capacity. We examined seven demosponge species (from high spicule skeleton contents to no spicules) commonly found along the central west coast of India for structural components, such as total inorganic contents (spicule skeleton and foreign inclusions), body density, porosity, and mesohyl TEM for the high microbial abundance/low microbial abundance status. Additionally, we estimated the sponge pumping rate by measuring the excurrent velocity, the abundance of individual pumping units and cells, i.e., choanocyte chambers and choanocytes, and also carried out a morphometric analysis of aquiferous structures. The excurrent velocity and the oscular flow rates showed a positive relationship with the oscular crosssectional area for all the study species. The inorganic spicule contents by their weight as well as volume formed a major component of tissue density and higher proportions of spicules were associated with reduced aquiferous structures and lower pumping rate. The ash mass% and the ash free dry weight (AFDW %) in the sponge dry mass showed separate and distinct associations with aquiferous system variables. For example, the number of choanocytes per chamber showed a wide difference between the studied species ranging from 35.02 ± 2.44 (C. cf. cavernosa) to 120.35 ± 8.98 (I. fusca) and had a significant positive relationship with AFDW% and a negative relationship with ash mass%. This study indicates that the differences in the proportions of structural components are closely related to sponge gross morphology, anatomy, and probably body contractions, factors that influence the sponge pumping capacity.

Hydrodynamic characteristics of aquiferous modules in the demosponge Halichondria panicea

ABSTRACTMulti-oscula sponges are organisms composed of aquiferous modules, each of which draws water through its canal system by means of pumping units (choanocytes, Cs, in choanocyte chambers, CCs) such that the filtered water leaves the module as an exhalant jet through the osculum of the module. Here we compare relations between the characteristic parameters of sponge volume (V), osculum cross-sectional area (OSA), exhalant jet speed (U0), and filtration rate (F) of single-osculum explants and individual aquiferous modules of multi-oscula explants of the demosponge Halichondria panicea. The latter modules are identified by observing from which osculum the surface administered dye will emerge. There is fair agreement in results between the two types of modules. For both types, the filtration rate is a linear function of the modules’ volume, with average values of volume-specific filtration rate (FV) of 1.8 and 1.2 ml min−1 cm−3 for single- and multi-oscula sponge explants, respectively. This and data from the literature for 5 demosponges support the hypothesis that the density of pumping units are of the same order of magnitude for the present given species and for some other demosponges.

Temperature‐ and size‐associated differences in the skeletal structures and osculum cross‐sectional area influence the pumping rate of contractile sponge Cinachyrella cf. cavernosa

AbstractSponges alter the proportion of structural and morphological components such as spicule skeleton and number of oscula in response to environment, development and growth. Such mechanisms indicate morphological and physiological variations within populations. We measured the pumping rate of different sized specimens of contractile sponge Cinachyrella cf. cavernosa present in the intertidal rock pools, during morning and afternoon low tides along the central west coast of India. Additionally, we measured the exhalant opening (oscular cross‐sectional area—OSA), tissue density, spicule skeleton weight and the abundance of choanocyte chambers to assess the morphological variations. Water temperature and sponge size showed a significant positive effect on pumping rate. OSA and the number of oscula increased with sponge size, but the sponge volume‐specific pumping rate did not increase (0.029 ± 0.020 ml/s ml‐1). Histological sections showed the abundance of chaonocyte chambers increased marginally with the sponge size, but the contraction state affected the count. Both tissue density and spicule skeleton weight were positively correlated with sponge size, particularly the increase in the size and number of spicule bundles radiating from the centre indicated a denser core in larger specimens. The subcortical lacunae and the peripheral choanosome with high abundance of canals appear to be the major volume reduction zones during contraction events. Our results indicate that the size and number of spicule bundles increase with sponge volume and the variation in temperature, contraction state, and size and number of oscula influence the pumping rate of C. cf. cavernosa.

Histological and ultrastructural features of Aplysina cauliformis affected by Aplysina red band syndrome

AbstractAplysina red band syndrome (ARBS) affects shallow–water branching Caribbean sponges of the genus Aplysina. Signs of ARBS consist of a red band that advances from an initial circular lesion in both directions along the branch of the sponge, leaving behind spongin fibers devoid of living tissue. The red band is dominated by the filamentous cyanobacterium Leptolyngbya sp., which is responsible for the red coloration, although its role in the etiology of ARBS remains elusive. We used a combination of histology and transmission electron microscopy to describe ultrastructural and cellular differences between healthy and diseased individuals of Aplysina cauliformis. Tissue from the red band adjacent to spongin fibers devoid of living tissue was compared to healthy‐appearing tissue on the same sponges and to healthy sponges. ARBS‐affected tissue exhibited changes in cell densities, with increases in archaeocytes, collencytes, and unidentified round eukaryotic cells; decreases in exopinacocytes, granular cells, and spherulous cells; and loss of intact choanocyte chambers. Archaeocytes associated with diseased tissue appeared to be more active, as indicated by increased numbers and lengths of pseudopodia, and by a higher density of engulfed bacteria and symbiotic cyanobacteria, some of which were in various stages of disintegration. Filaments of Leptolyngbya sp. tended to be associated only with the ectosome of the red band portion of the lesion itself, and were rarely observed infiltrating intact tissue. These descriptions of anatomical and cellular responses to ARBS in A. cauliformis add to our understanding of the pathological effects of this widespread disease.

Hydrodynamics of the leucon sponge pump.

Leuconoid sponges are filter-feeders with a complex system of branching inhalant and exhalant canals leading to and from the close-packed choanocyte chambers. Each of these choanocyte chambers holds many choanocytes that act as pumping units delivering the relatively high pressure rise needed to overcome the system pressure losses in canals and constrictions. Here, we test the hypothesis that, in order to deliver the high pressures observed, each choanocyte operates as a leaky, positive displacement-type pump owing to the interaction between its beating flagellar vane and the collar, open at the base for inflow but sealed above. The leaking backflow is caused by small gaps between the vaned flagellum and the collar. The choanocyte pumps act in parallel, each delivering the same high pressure, because low-pressure and high-pressure zones in the choanocyte chamber are separated by a seal (secondary reticulum). A simple analytical model is derived for the pump characteristic, and by imposing an estimated system characteristic we obtain the back-pressure characteristic that shows good agreement with available experimental data. Computational fluid dynamics is used to verify a simple model for the dependence of leak flow through gaps in a conceptual collar-vane-flagellum system and then applied to models of a choanocyte tailored to the parameters of the freshwater demosponge Spongilla lacustris to study its flows in detail. It is found that both the impermeable glycocalyx mesh covering the upper part of the collar and the secondary reticulum are indispensable features for the choanocyte pump to deliver the observed high pressures. Finally, the mechanical pump power expended by the beating flagellum is compared with the useful (reversible) pumping power received by the water flow to arrive at a typical mechanical pump efficiency of about 70%.

Anatomy and ultrastructure of the tropical sponge Cladocroce caelum (Haplosclerida, Demospongiae).

The main characteristic of sponges (Porifera) is the presence of the aquiferous system-a system formed by canals and choanocyte chambers, in which the sponges carry out most of their physiological functions. Despite of the importance for the biology of the group, the knowledge about this structure is still incipient, even when morphological investigations are taken in account. Here, we investigated the anatomy and ultrastructure of the tropical demosponge Cladocroce caelum (Haplosclerida, Demospongiae) using light and electron microscopy. In the studied region, specimens of this species were repent or repent-branched, possessing one to several oscula. A uniform and reduced atrium was found just below each osculum. There was a thin ectosome and the choanosome presented meager mesohyl, but a high number of choanocyte chambers. The choanocyte chambers were rounded, and, as in other haplosclerids, they are found separated from the mesohyl by endopinacocytes, "hanging" in the inhalant canals. Even though the utility of the general organization of the aquiferous system has been advocated as a possible tool to understand the phylogeny of the group, we found that these characters might not be as useful as expected. The size of the particles ingested by the sponge and the amount of bacteria to sustain their bodies are discussed. In addition, we found that the density of choanocyte chambers was reduced when the specimens were carrying out the spermatogenesis, indicating that the reproduction may impair the filtering activity of the sponge. Our findings consist in a first step to better comprehend the physiology, development, and adaptation to the environmental conditions where the species is found.

Exhalant jet speed of single-osculum explants of the demosponge Halichondria panicea and basic properties of the sponge-pump

Sponges are modular organisms in which each aquiferous module draws water through a canal system by means of pumping units (choanocyte chambers, CC), and the filtered water leaves the module as an exhalant jet through a single opening (osculum). A constant density of CCs in sponges would imply that the filtration rate must be proportional to the sponge volume, but it is less obvious how the osculum cross-sectional area (OSA) scales to sponge volume. Here, we present data obtained on single-osculum sponge explants (i.e. single aquiferous modules) of the demosponge Halichondria panicea to gain insight into important basic properties of the sponge-pump. In the experimental study of 27 explants (volume Vs = 14 to 1977 mm3), osculum cross sectional area (OSA), exhalant jet speed (U0) and filtration rate (F = OSA × U0) were measured. The observed scaling with size (OSA ~ Vs0.66; U0 ~ OSA0.45; F ~ OSA1.45) was found to be close to that inferred from the hypothesis of volume based CC density. Thus, the volume-specific filtration rate (= pumping rate) could be approximated as F (ml min−1) ≈ 2.3Vs (cm3) which is of the same order of magnitude as that of the demosponge Haliclona urceolus, F (ml min−1) ≈ 3.5Vs (cm3). This suggests that for the two sponge species CCs are very likely of similar size, with similar individual pumping rate, and of similar uniform distribution over the sponge volume. By comparing the observed increase of U0 with increasing OSA to literature data on other leuconoid sponge species this revealed a power function with an identical exponent 0.45 and maximum values of U0 = 6 to 8 cm s−1. This indicates that U0 of a single-osculum explant, or U0 of an individual osculum in a multi-oscula sponge approaches an upper limit as the sponge grows, implying that a module of a multi-oscula sponge may increase only to a certain size. Time-lapse video-microscope recordings of sponge explants showed temporal variation in OSA during spontaneous contractions. Exposure to a neurotransmitter (GABA) as well as overloading with ink particles triggered contractions that correlated with both decreasing OSA and U0 that eventually became zero. Video-microscope recordings revealed that it was contraction of the endopinacoderm lining the excurrent canals that effectively restricted or stopped the water flow.

Description of the first Caribbean Oscarellidae (Porifera: Homoscleromorpha)

The sponge class Homoscleromorpha has a challenging taxonomy and its systematics is still a matter of debate. A significant effort has recently been deployed to better evaluate the diversity of these sponges, and each new exploration of cryptic habitats reveals new species. Although several undescribed or wrongly determined Oscarella-like sponges have been reported by different authors, the Oscarellidae family still lacks description of its true Caribbean representatives. The exploration of various submarine caves in the Lesser Antilles has allowed us to find and to formally describe the first two Oscarellidae of the Caribbean Sea, Oscarella filipoi sp. nov. and Oscarella zoranja sp. nov. Both new species are quite common in semi-dark habitats throughout the Lesser Antilles. Moreover, O. filipoi sp. nov. is the largest Oscarellidae ever observed world-wide. Both species harbor a sylleibid aquiferous system and a high density of ovoid to spherical choanocyte chambers. The molecular taxonomy clearly shows their affiliation to the Oscarella clade containing the type species of the Oscarellidae family. In addition to their growth forms, these two species differ in the shape of their mesohylar cells, and in the degree of development of their basal region. This latter trait is particularly remarkable in large specimens of O. filipoi which can have a very thick ectosome.

Asexual and puzzling sexual reproduction of the Mediterranean sponge Haliclona fulva (Demospongiae): life cycle and cytological structures

AbstractDespite the common assumption that most Haplosclerida are viviparous sponges, this study of the reproductive cycle of Haliclona fulva demonstrates that this species is actually oviparous and gonochoric. Intriguingly, not a single male was recorded in 15 months of sampling. Oogenesis is synchronous, starting in late April and terminating in September. Asexual reproduction is represented by cyclic budding, which occurs from late November to early March. During the season of asexual reproduction, the reproductive effort represents from 0.21% to 1.49% of the parental tissue, with the highest values being recorded in winter. During the season of sexual reproduction, the female reproductive effort ranges 0.05–1.15%, with the highest effort appearing in early summer. However, no significant correlation between reproductive efforts and seawater temperature fluctuations could be detected. We describe the ultrastructural morphogenesis of the buds for the first time in this species. This process is asynchronous, with buds of variable size being attached to the maternal apical surface via a short stalk. Young buds lack any particular anatomical organization, whereas bud maturity is characterized by the development of mesohyl and by the appearance of an increasing number and volume of lacunae in the central part of each bud. At this stage, buds harbor numerous small choanocyte chambers scattered throughout the inner region, and all cell types known from the mesohyl of parental sponges: microgranular cells, granular cells, archaeocytes, endopinacocytes and exopinacocytes, central cells, and sclerocytes.

Distinct histomorphology for growth arrest and digitate outgrowth in cultivated Haliclona sp. (Porifera: Demospongiae).

The use of sponges in biotechnological processes is limited by the supply problem, and sponge biomass production is becoming a current topic of research. The distinction between characteristics for growth and growth arrest is also important for environmental monitoring. In this study, we analyze the morphology of the digitate outgrowths from the sponge Haliclona sp. The sponge Haliclona sp. was successfully cultivated for 14 months in a closed system. The morphological characterization of growth arrest was performed after submitting explants to starvation-stress for approximately 2 weeks, to correlate morphology with growth and growth arrest. The digitate outgrowth showed three distinct regions: mature (MR), transition (TR) and immature (IR). Our data suggest a growth developmental program, with collagen fascicles guiding axial growth in IR, followed by progressive development of choanocyte chambers and large aquiferous systems at the more mature proximal region (choanosome). The intercalation of choanocyte chambers and small aquiferous systems inside collagen fascicles previously originated at the IR region can be responsible for thickening expansion and conversion of the collagen fascicles into columnar choanosome in MR. The growth arrest after starvation-stress assay showed morphological changes in the IR corroborating collagen in the extreme tip of the digitate outgrowth as an important role in guiding of axial growth of Haliclona sp. The identification of distinct morphologies for growth and growth arrest suggest a growth developmental program, and these data could be useful for further investigations addressing sponge biomass gain and environmental monitoring.

The ontogeny of choanocyte chambers during metamorphosis in the demosponge Amphimedon queenslandica.

BackgroundThe aquiferous body plan of poriferans revolves around internal chambers comprised of choanocytes, a cell type structurally similar to choanoflagellates. These choanocyte chambers perform a range of physiological and developmental functions, including the capture of food and the generation of stem cells. Despite the increasing interest for choanocytes as sponge stem cells, there is limited knowledge on the development of choanocyte chambers. Using a combination of cell lineage tracing, antibody staining and EdU labeling, here we examine the development of choanocytes and the chambers they comprise during metamorphosis in the marine demosponge Amphimedon queenslandica.ResultsLineage-tracing experiments show that larval epithelial cells transform into mesenchymal pluripotent stem cells, resembling archeocytes, within 24 h of initiating metamorphosis. By 36 h, some of these labeled archeocyte-like cells have differentiated into choanocytes that will form the first postlarval choanocyte chambers. Non-labeled cells also contribute to these primary choanocyte chambers, consistent with these chambers being a chimera of multiple transdifferentiated larval cell types and not the proliferation of a single choanocyte precursor. Moreover, cell proliferation assays demonstrate that, following the initial formation of choanocyte chambers, chambers grow at least partially by the proliferation of choanocytes within the chamber, although recruitment of individual cells into established chambers also appears to occur. EdU labeling of postlarvae and juveniles reveals that choanocyte chambers are the primary location of cell proliferation during metamorphosis.ConclusionOur results show that multiple larval cell lineages typically contribute to formation of individual choanocyte chambers at metamorphosis, contrary to previous reports in other species that show sponge choanocyte chambers form clonally. Choanocytes in postlarval and juvenile A. queenslandica chambers can also divide, with choanocyte chambers being the primary location of cell proliferation. Interestingly, the level of cell proliferation varies greatly between chambers and appears to be contingent on the size, location and developmental state of the chamber. Small chambers on the periphery of the body tend to possess more dividing cells. As choanocytes can also dedifferentiate into archeocyte-like cells, cell proliferation in chambers may not only contribute to chamber growth and self-renewal but also increase the number of pluripotent archeocytes.

Some aspects in the life cycle of freshwater sponges (Spongillidae, Porifera) from open Lake Baikal

A histological analysis of the tissue structure in different species of Baikal sponges was performed. The material was collected at a depth of 3–4 m at the Berezovyi test site (southern Lake Baikal) in various seasons of 2001–2003. During the entire year, representatives of the family Lubomirskiidae had a well-developed irrigation system with numerous choanocyte chambers. In Trochospongilla sp. (Spongillidae) from open Baikal, such a tissue pattern was observed only during the summer time. Annually, these sponges undergo tissue regression, i.e., a reduction of the irrigation system accompanied by changes in the cell composition in autumn with subsequent recovery in spring. The onset and termination of tissue regression are adapted to the environment of Lake Baikal.

Transdifferentiation is a driving force of regeneration in Halisarca dujardini (Demospongiae, Porifera).

The ability to regenerate is widespread in the animal kingdom, but the regenerative capacities and mechanisms vary widely. To understand the evolutionary history of the diverse regeneration mechanisms, the regeneration processes must be studied in early-evolved metazoans in addition to the traditional bilaterian and cnidarian models. For this purpose, we have combined several microscopy techniques to study mechanisms of regeneration in the demosponge Halisarca dujardini. The objectives of this work are to detect the cells and morphogenetic processes involved in Halisarca regeneration. We show that in Halisarca there are three main sources of the new exopinacoderm during regeneration: choanocytes, archaeocytes and (rarely) endopinacocytes. Here we show that epithelial-to-mesenchymal transition (EMT) and mesenchymal-to-epithelial transition (MET) occur during Halisarca regeneration. EMT is the principal mechanism during the first stages of regeneration, soon after the injury. Epithelial cells from damaged and adjacent intact choanocyte chambers and aquiferous canals assume mesenchymal phenotype and migrate into the mesohyl. Together with archaeocytes, these cells form an undifferentiated cell mass beneath of wound, which we refer to as a blastema. After the blastema is formed, MET becomes the principal mechanism of regeneration. Altogether, we demonstrate that regeneration in demosponges involves a variety of processes utilized during regeneration in other animals (e.g., cell migration, dedifferentiation, blastema formation) and points to the particular importance of transdifferentiation in this process. Further studies will be needed to uncover the molecular mechanisms governing regeneration in sponges.